This invention relates to methods and apparatus for fixing toner particles to a receiver in an electrostatographic apparatus. More particularly, this invention relates to methods and apparatus for fusing toner particles to a receiver to provide a fused toner image with desirable gloss characteristics.
Heat-softenable toners are widely used in imaging methods such as electrostatography, wherein electrically charged toner particles are deposited imagewise on a dielectric or photoconductive element bearing an electrostatic latent image. Most often in such methods, the toner is then transferred to a surface of another substrate, such as, e.g., a receiver sheet comprising paper or a transparent film, where it is then fixed in place to yield a final desired toner image.
When heat-softenable toners, comprising for example thermoplastic polymeric binders, are employed, the usual method of fixing the toner in place involves applying heat to the toner once it is on the receiver sheet surface to soften it, and then allowing or causing the toner to cool.
One such fusing method comprises passing the toner-bearing receiver sheet through a nip formed by a pair of opposing members, typically in the form of cylindrical rollers, wherein at least one of the members (usually referred to as a fuser member) is heated and contacts the toner-bearing surface of the receiver sheet in order to heat and soften the toner. The other member (usually referred to as a pressure member) serves to press the receiver sheet into contact with the fuser member. In some other fusing methods, the configuration is varied and the xe2x80x9cfuser memberxe2x80x9d or xe2x80x9cpressure memberxe2x80x9d can take the form of a flat plate or belt.
The desired gloss of the fused electrostatographic images can vary depending on the thermoplastic binder used for the toner, the materials used for the surfaces of the fuser and/or pressure members, and conditions employed during the fusing step as mentioned briefly hereinafter. Typically, it is preferred that multicolor pictorial images have a glossy finish and monochromatic text and graphics have a matte finish.
Several methods for imparting glossy or matte finishes to an image have been disclosed. One method is to cover a multicolor toner image with clear, glossy toner. The clear toner can be laid down in an image configuration or it can be laid down uniformly over the whole image. See, for example, Crandall, U.S. Pat. No. 4,828,950 and Ng, U.S. Pat. No. 5,234,783.
Another method to provide glossy pictorial toner images, produced in an undercolor removal apparatus, is to lay a black matte toner down first and completely cover it by a color (cyan, magenta, yellow) toner having a more glossy finish after fusing. Examples of such methods are described in Japanese Patent Application No. 133422/87, Laid Open No. 300254/88, Dec. 7, 1988. Additional references which disclose the use of glossy and matte toner combinations include Japanese Patent Application No. 90JP-333829, Laid Open No. C92-132261, and U.S. Pat. Nos. 5,162,860 and 5,256,507.
The use of different fuser rollers or finishing apparatus to effect the gloss of a fused toner image has been considered. It has been disclosed that hard metallic rollers covered with a fluorocarbon resin can be used to produce fused toner images having high gloss. On the other hand, most soft rubber coated rollers impart a matte finish to fused images.
U.S. Pat. No. 5,118,589 discloses the use of pressure members with a predefined surface finish to impart either gloss or texture to a heat softenable layer of a receiver onto which color toner particles have been thermally transferred. The use of textured pressure members to impart texture to fixed toner images has also been disclosed in U.S. Pat. Nos. 4,258,095 and 5,085,962. U.S. Pat. No. 5,019,869 discloses an electrophotographic device in which a finish is applied to a toner image by selecting one of a plurality of finishing rollers, each roller having a different and distinct surface texture. Further, U.S. Pat. No. 5,319,429 illustrates the use of a fusing apparatus comprising two endless belts each having a glossy surface to provide glossy images.
U.S. Pat. No. 4,639,405 discloses an apparatus for providing glossy fused toner images which passes toner-bearing receivers sequentially through a first and second pair of rollers, the first pair of rollers fuses the toner, and the second pair of rollers provides gloss to the toner image.
Another method for affecting the gloss of an electrophotographic image is to change the toner binder resin rheology, and therefore, the melt flow characteristics of the toner composition. A toner which has higher melt flow properties at a given temperature, provides higher image gloss as compared to a toner formulation which has lower melt flow properties. Because the melt viscosity of a polymer changes as a function of the weight average molecular weight, substantial changes in the melt viscosity of a toner can be achieved by controlling the molecular weight of the toner binder. References which disclose that changing the molecular weight can affect the gloss include U.S. Pat. Nos. 4,913,991 and 5,258,256.
The amount of crosslinking in the toner binder polymer also can affect gloss. Typically, toners having high crosslinked polymer binders provide matte images. An example of such toner for the purpose of providing a low gloss image is detailed in U.S. Pat. No. 5,395,723.
U.S. Pat. No. 5,334,471 teaches a method of controlling gloss in an electrophotographic toner image by utilizing light-scattering particles of a specific size range. The light-scattering particles are large enough to provide a bumpy image surface which is said to impart low gloss.
As described above, in electrostatographic processes using toners, matte or glossy finishes of the fused toner image can be provided either by controlling the rheological behavior of the toner binder polymer or by controlling the surface texture of the fusing members. However, even with these methods and materials, it has not been heretofore possible to control or otherwise adjust. the gloss of a fused toner image so as to reduce the level of differential gloss within a fused toner image. Such an advantage would be particularly desirable for process color machines which employ development stations that utilize a plurality of toner compositions with differing colors. Typically, the toner compositions, after they are fused to the receiver, can form areas within the toner image which exhibit a different level of gloss relative to another area of the toner image. The result is a fused toner image having areas that appear glossier than other areas within the image, and therefore, the overall look of the image is not as visually pleasing to the human eye. It would be desirable to reduce this xe2x80x9cdifferential glossxe2x80x9d within the image, so that the resulting image is better in appearance and more closely resembles the image quality of a lithographic print.
Furthermore, an operator of an electrostatographic printing machine may desire, from time-to-time, to adjust the overall gloss of a toner image without changing the fusing system of the machine. For example, a special print job may require a different overall gloss level (either higher or lower) in comparison to the gloss which can be typically provided by the fusing system used therein. It would be desirable to have a capability to adjust the level of gloss to meet the specifications for the job without changing the fusing system.
Therefore, as can be seen, a need exists for methods and apparatus to produce fused toner images having reduced differential gloss, i.e., gloss levels which are relatively uniform within the image, and also the overall gloss of the image to meet the specifications for a particular job.
The foregoing objects and advantages are attained by the present invention, which in one aspect, concerns apparatus for adjusting gloss of a toner image fused to a receiver medium. In an embodiment, the apparatus comprises:
a finishing member which contacts the toner image on the receiver medium, the finishing member comprising an outer layer having a contact surface thereon comprised of a fluorocarbon thermoplastic random copolymer co-cured with a fluorinated resin;
a pressure member positioned adjacent to and in contact with the outer contact surface of the finishing member such that a pressure nip is formed between the contact surface of the finishing member and the pressure member; and
a heat source for transferring heat to at least one of the finishing member and the pressure member so that heat is transferred to the toner image under pressure while the toner image is passed through the pressure nip.
In another aspect, the invention relates to apparatus for fusing a toner image to a receiver medium. The apparatus comprises:
a fusing system for fusing the toner image to the receiver medium so as to provide a fused toner image on the receiver medium, and
a post-fusing finishing system for adjusting gloss of the fused toner image, the post-fusing finishing system comprising a finishing member which contacts the fused toner image so as to transfer heat thereto under pressure, the finishing member comprising an outer layer having a contact surface thereon including a fluorocarbon thermoplastic random copolymer co-cured with a fluorinated resin.
In another aspect, the present invention relates to a method of fusing a toner image to a receiver medium. The method comprises the steps of:
fusing a thermoplastic toner composition to a receiver medium to provide a fused toner image thereon having an initial amount of gloss; and
contacting the fused toner image with a finishing surface comprised of a fluorocarbon thermoplastic random copolymer co-cured with a fluorinated resin, the contact being under conditions of temperature and pressure such that gloss of the fused toner image is adjusted thereby.
Additionally, the invention also relates to a method for adjusting gloss of a fused thermoplastic toner image having an initial amount of gloss. The method comprises contacting the fused thermoplastic toner image with a finishing surface comprised of a fluorocarbon thermoplastic random copolymer co-cured with a fluorinated resin. The contact is under conditions of temperature and pressure such that gloss of the fused toner image is adjusted thereby.
In preferred embodiments, the fluorocarbon thermoplastic random copolymer co-cured with the fluorinated resin includes subunits of:
xe2x80x94CH2CF2)xxe2x80x94, xe2x80x94(CF2CF(CF3))yxe2x80x94, and xe2x80x94(CF2CF2)zxe2x80x94,
wherein:
x is from 1 to 50 or 60 to 80 mole percent,
y is from 10 to 90 mole percent,
z is from 10 to 90 mole percent, and
x+y+z equals 100 mole percent.
In other embodiments, the fluorocarbon thermoplastic random copolymer co-cured with the fluorinated resin is the reaction product of a mixture comprising a fluorocarbon thermoplastic random copolymer, a curing agent having a bisphenol residue, a reactive filler including zinc oxide, a fluorinated resin, and an aminosiloxane.
The foregoing aspects of the invention are discussed in more detail hereinbelow.